Prior art workers have devised numerous types of electrical output panels having two or more receptacles for use with single conductor cable connectors. While their use is by no means so limited, such panel assemblies are employed in lighting and sound applications for theatrical and concert productions, circuses, television studios, movie studios and the like. It will be understood that lighting equipment and sound equipment require a multitude of connections. Single conductor connectors are preferred because cable for multiple conductor connectors is generally characterized by large diameter, considerable weight, and is difficult to maneuver and transport.
Prior art workers have recognized that when dealing with single conductor connectors, it is important that each individual connector be connected only with its intended receptacle. Color coding and various types of indicia are helpful in this respect, but they do not preclude error. As a result, prior art workers have devised polarizing means which make it physically impossible to mate a connector with any receptacle other than its intended receptacle.
It is further important, both to protect the equipment and as a safety factor, to connect and disconnect a series of connectors to and from the panel assembly in a particular order. For example, where a ground is used, it is generally desirable that the ground makes first and brakes last. As a result, prior art workers have devised panel assemblies provided with interlocking devices requiring the connectors to be mated with their respective receptacles in a given order and disconnected therefrom in the reverse of that order. Examples of panel assemblies provided with polarizing means and interlocking devices are taught in copending application Ser. No. 07/067,239, filed June 25, 1987 in the names of David C. Kamp and Albert P. Newman, now U.S. Pat. No. 4,767,347 and entitled ELECTRICAL PANEL ASSEMBLY. The teachings of this application are incorporated herein by reference.
When a panel assembly of the type under discussion is used as an output panel, there is a third important factor to consider to prevent damage to equipment being connected to the panel assembly, the panel assembly itself, and for safety reasons. When the cable connectors are being connected to the panel assembly, or are being disconnected therefrom, the power source to which the panel is connected should be turned off. Prior art workers have approached this problem by providing, as optional equipment, a limit switch in association with the last receptacle and a magnetic circuit breaker. While this works well, the elements required are extremely expensive and this type of safety system adds considerably to the cost of the equipment.
The present invention is based upon the discovery that a safety system to prevent powered connection or disconnection can be provided quite inexpensively. The safety system of the present invention is simple in construction, inexpensive to install, and foolproof. The safety system will prevent release of the panel interlock elements by the ground connector so long as the panel has voltage applied to its receptacles. Further, the safety system will prevent disconnection of the last power connector so long as there is voltage applied to the panel receptacles.
As will be apparent to one skilled in the art, the teachings of the present invention, with appropriate modifications, can be applied to any multiple receptacle output panel assembly having mechanical interlocking elements determining the order of connection and disconnection of the cable connectors to and from the panel. For purposes of an exemplary showing, the present invention will be taught in its application to the preferred panel embodiment of the above-mentioned copending application.